1. Field of the Invention
This invention relates to improvements in trucks for railroad vehicles, especially locomotives. More particularly, the invention relates to improved pedestal liners for those portions of the trucks which are slideably engaged to enable the wheels in the body of the locomotive to move relative to each other in a generally vertical direction.
2. Background of the Invention
The truck upon which a locomotive is supported comprises two side frames tied together by a transverse member known as a bolster. One type of truck commonly used for locomotives is referred to as a pedestal truck. The pedestals are part of the side frames and are formed in inverted U-shaped sections that horizontally position and hold a journal box to move essentially vertically in relationship to the truck. Two projections that comprise the U of the pedestal are called the pedestal legs and the space between them, the jaw. The jaw is closed at the bottom when the journal is inserted by means of a pedestal tie bar. In this manner, the journal box is held positioned in a vertical sliding relationship with the truck. As the locomotive body is supported by the bolster and side frames, vertical movement between the locomotive body and journal box, journal and wheels is permitted.
Considerably wear takes place at the interface between the pedestal and the journal box. Wear plates are attached to both the pedestal legs and journal boxes to reduce wear and protect the underlying parts. The wear plates attached to the pedestal legs are generally referred to as pedestal liners.
These pedestal liners have traditionally been made of a very hard low wear steel, such as manganese steel. The manganese steel is fitted to the guides with clearance, to allow the axle box to move up and down in response to the springing action provided in the suspension system. Frequently mating manganese steel plates are fixed to the axle box to reduce overall wear, but the problem with this system is, of course, that whenever steel runs against steel, wear takes place on both surfaces.
In more recent years, it has been found that much less wear occurs by using wear plates made from a tough plastic material, such as nylons, polyacetals, polyolefins, polycarbonates, polyethers, polyesters, polyurethanes, etc. as disclosed in U.S. Pat. No. 3,554,618. In particular, nylon pedestal liners have gained a degree of acceptance through the industry primarily because they outwear steel liners. The plastic liners also have the advantage of reducing the wear on mating metal surfaces such as pedestal legs and journal boxes.
While the plastic pedestal liners have in general proved to be considerably more satisfactory than the steel alloy liners, they do have disadvantages. For instance, they sometimes fail by cracking adjacent to those areas where they are bolted on to the pedestal. It is believed that under conditions of heavy use, the plastic liners may fracture due to the fatigue stress acting on liners to the point where they are secured to the pedestal leg. This stress cracking may become particularly pronounced under extreme cold winter conditions. To try to overcome this problem, U.S. Pat. No. 4,094,253 suggests that the pedestal liners not be secured to the pedestal legs but permitted to float. This has not been found to be altogether satisfactory and U.S. Pat. No. 4,170,180 suggests other possibilities for trying to fasten a cast nylon pedestal liner while avoiding the fastening problems discussed above.
U.S. Pat. No. 3,554,618 discloses a two piece pedestal liner assembly using a metal support with a plastic wear surface area. The face of the backing plate contains a large hole within which is placed the nylon wear plate, but in this arrangement the nylon is ineffective in carrying or distributing the applied load. Consequently, the area of nylon left incapable of carrying the load is pressurized more highly than it ought to be. Thus, it will be seen that all of the designs either using steel pedestal liners, cast plastic pedestal liners or combined steel and plastic pedestal liners available to date have serious disadvantages.
It is the object of the present invention to produce a pedestal liner in which a polymeric wear resistance layer is cast and polymerized directly on a steel backing plate such that the polymer is firmly bonded to the backing plate.